Many drugs must be administered parenterally, because they are either not resorbed sufficiently or destroyed in the gastrointestinal tract. Typical examples include peptide drugs like insulin. Therefore, in the following the invention is described in the context of an insulin pen, although it extends to other drug delivery devices and drugs.
The pharmacological half-life of these drugs often is very short, leaving the need for multiple daily injections. Therefore, often the injections are performed by the patient himself instead of trained medical professionals. An insulin-dependent diabetic patient e.g. needs to inject multiple times a day at variable doses, adjusted to food intake and physical activity.
To comfort these frequent variable dose self-administrations drug delivery devices have been introduced that are easy to use and typically comprise a reservoir with a plunger, a hypodermic needle and a dosing mechanism. A typical example for such devices is called an “insulin pen”. These pens are critical medical devices for the reason that both an overdose and underdose can lead to severe health problems including death. Therefore, those devices are mostly kept very reliable and independent of e.g. battery charge. Most insulin pens on the market today have a strictly mechanic dosing mechanism.
While these injection pens facilitate the multiple injections required, it is difficult and cumbersome for the patient to keep records of all parameters determining the insulin dose adjustment required. Even keeping track of the injection time and dose itself becomes a demanding task, since the typical drug delivery devices do not include means for data communication nor memory. Therefore, it is not rare that a patient does not remember dose, time or the sheer fact of injection in daily life. Severe effects of overdosing or omitted administrations are therefore not rare events and threaten health and life of these patients.
Further, a patient may use one, two or even three different pens during the day. A typical example for a dosage pattern is as follows: In the morning the patient injects a dose of long-lasting insulin with his/her first pen. During the day he/she further injects multiple doses of rapid acting insulin before each meal using a different pen. Timing and doses are typically similar from day to day for the same patient. Deviation from this pattern would be dangerous. The wrong pen/insulin type could be used or the wrong dose injected, or the injection either forgotten or doubled.
In the prior art, DE-A1-10 2004 040 441 discloses a method for determining the filling level of a substance in an ampoule comprising at least two electrodes, whereby the filling level is determined by measuring the capacity of at least one condenser which is formed by said at least two electrodes. According to this publication, the electrodes are located directly in an injection device containing the ampoule, or, preferably, the electrodes are located on the ampoule, in particular are integrated into the ampoule.
As a consequence, the disclosure of DE-A1-10 2004 040 441 requires an integration of electronics into the injection device, making the device more complex and failure prone. For example, the function of the injection device will depend on the availability of a charging current, or a charged power source, and, therefore, will be less reliable than a classical injection device (e.g. insulin pen) with a mechanical dosing mechanism.
WO-A1-2013138830 describes a capacitive NFC (Near Field Communication)-based fill-level sensor for insulin pens. This publication is based on the same technical principle for determining the filling level of the insulin in an ampoule as shown in DE-A1-10 004 040 441. For this purpose, at least two electrodes are located on the ampoule or directly inside of the part of the pen holding the ampoule.
The invention disclosed in WO-A1-2013138830 is inter alia defined by the presence of two antennas allowing the transmittance of measured values to an external data communications unit via NFC.
US-A1-20140018733 discloses a replaceable cap for a transdermal liquid dosing device such as an insulin pen. The cap body also includes a cavity opening into the interior of the cap body and housing a control unit which includes a timer unit, a switch mechanism and a timer display unit. This specific design of the interior of the cap body (control unit including timer unit, switch mechanism and timer display unit) is supposed to help the user determining whether a given dose has been administered. US-A-20140018733 is silent with respect to the applied quantity of the corresponding substance and to the (remaining) filling level of the substance in the dosing device.
US-A1-20020096543 discloses a portable control device to be mounted externally on a conventional injection pen cap containing a touchless proximity sensor that is located on one side of the cap to detect presence/removal either of the metal needle, the insulin ampoule or an electronic tag implemented in the pen. The control device also includes a transmitter that communicates with a console to control a system of colored lights as feedback and reminder for the patient. The disclosed embodiments are complex to use and learn and may require discarding or adapting the existing insulin delivery systems already in use by the patient. This disclosure is not suitable to achieve precise, sensitive and reproducible readout of the insulin ampoule content required for tracking of the applied dose, because it does not apply an electric field through the entirety of the insulin container homogenously and also does not comprise means to adjust for inhomogeneity or disturbances of said electric field.